Accessory dwelling units explained: what is an ADU and should you consider one?


Accessory Dwelling Units (ADUs) are getting a lot of buzz lately. If the term sounds like industry jargon, or perhaps makes you think of a purse large enough to live inside, maybe one of these will ring a bell: in-law suite, carriage house, granny flat, or a good old apartment over the garage.

What is an accessory dwelling unit?

ADUs are simply a secondary living space located on the same property as a traditional home, usually offering its own separate entrance. Generally, an ADU will have its own kitchen, bathroom, and living space, but the key element is that it can function as its own, separate space. An ADU can be a tiny house, a basement apartment, or an attic with its own entrance. Accessory Dwelling Units are a longstanding concept in America, but a recent resurgence due to population growth and untenable city real estate costs are making them an increasingly more attractive option for homeowners.

Why are ADUs becoming more popular?

There are four reasons for the growing popularity of ADUs:

  1. They’re a smart investment. You can make additional income renting the ADU on your property.
  2. They can increase your property value, as well as potential resale value. One study published in 2012 that surveyed 14 properties in Portland, Oregon with added ADUs found that ADUs generally contributed about 25%-34% to each property’s assessed value and added a 51% average increase in resale value. An additional living space is a very attractive addition to any property.
  3. They provide living space for loved ones. More and more, Americans are trending towards living in multigenerational homes, and want long term stability where they settle down. Having an additional living space on your property can allow aging parents, young adult children, or even close friends to be close by, but with the added benefit of privacy and separation.
  4. Last but not least, ADUs are versatile. A separate space can serve as an office, a gym, a guest house, or a playroom for young ones.

Determining the cost of an Accessory Dwelling Unit

The average cost of building an ADU ranges hugely based on where you live and what you’re working with. There are examples of recently built ADUS that cost as low as $18,000 all the way up to $400,000, but generally tend to start at $140,000 with an average square foot cost of $180-250. It depends on what you’re looking to do and what your space looks like—for instance, converting a basement is different than building a detached structure in your backyard.

At Landis, our range for creating a basement apartment in an unfinished basement is $100,000 to $300,000, and a new detached structure or building above a garage is $200,000 to $450,000.

How large is the typical ADU?

The typical ADU ranges between 600 and 1000 square feet in the United States (according to data from AARP). An ADU will generally accommodate a studio, one bedroom or two-bedroom dwelling and is ideal for housing 2 tenants or a family with one child. Of course, larger ADUs are also an option as the size of an ADU will be determined by the ample land available on your property.

The benefits of ADUs for the D.C. metropolitan area

Housing costs in Washington D.C. and its surrounding neighborhoods have been on the rise for the past decade and continue to climb today. Accessory Dwelling Units can help maximize your property, and in turn, help your community: “ADUs are a low-impact way to diversify housing options, provide more affordable homes for young families or older adults, and help the homeowner with additional income through rent” offers the Metropolitan Area Planning Council (MAPC).

Due to their small size, ADUs are a more sustainable, eco-friendly option as well. They require less energy and fewer resources, thus minimizing carbon emissions and utility costs. To quote Professor Karen Chapple in Frameworks, UC Berkeley’s College of Environmental Design magazine: “As infill development, [ADUs] make efficient and ‘green’ use of existing infrastructure and help increase densities to levels at which transit becomes viable — yet with lower costs and quicker permitting processes than for larger, multi-family building types.”

In addition, zoning code changes have made it easier to build ADUs in D.C., and the Coalition for Smarter Growth, a D.C. area organization puts it best: “By building ADUs across the city, we can weave additional housing into residential neighborhoods in ways that enhance the community fabric, promote intergenerational living arrangements, and improve housing affordability.”

Happily, Landis has been building ADUs in the Washington D.C. metropolitan area for years, and since we handle all aspects of the construction process in-house, we can take care of the permitting, regulations, zoning, etc. involved for you!

For those wanting to rent out their ADUs commercially it’s important to understand the D.C. rules and regulations around renting ADUs. Landis is not a certified provider of ADU licensing for rentals but can still help you achieve your dream ADU for personal, family or friend accommodations.